1. Field of Invention
The present invention provides a novel class of borane-sulfide hydroboration agents, their methods of production and their use in the hydroboration and reduction of organic compounds. More particularly, this invention provides novel borane dialkyl and alkoxyalkyl sulfides which have a number of advantages over the presently available agents.
2. Prior Art
Borane-tetrahydrofuran is a valuable reagent for the hydroboration of olefins and for the reduction of organic compounds. It suffers from the disadvantage in that the solutions are unstable over a period of time. U.S. Pat. No. 3,882,037 discloses stabilized borane-tetrahydrofuran solutions which permit storage of such solutions for relatively longer periods of time. However, the inherent availability only as a relatively dilute solution in tetrahydrofuran poses a serious drawback to the commercial use of this reagent.
Borane-methyl sulfide (BMS) is much more stable than borane-tetrahydrofuran and is widely used for both hydroboration and reduction [See Burg et al., J. Am. Chem. Soc. 76, 3307 (1954) and Coyle et al., J. Am. Chem. Soc. 81, 2989 (1959)]. However, it suffers from the serious disadvantage in that it yields a product which contains free dimethyl sulfide. The free dimethyl sulfide is highly volatile, b.p. 38.degree. C., flammable and has a very noxious odor. Moreover, it is not soluble in water, so it cannot be disposed of by washing it away with water.
Borane-1,4-thioxane (U.S. Pat. No. 4,298,750) is another valuable hydroboration agent. It has both lower volatility and milder odor than dimethyl sulfide. It has a limited solubility in water and can be easily oxidized to the corresponding sulfoxide, which is miscible in water. This agent is a liquid, 8M in BH.sub.3, stable over prolonged periods. Unfortunately, this commercially available reagent is relatively costly compared to borane-tetrahydrofuran and borane-dimethyl sulfide. The growing importance of borane reagents for the synthesis of pharmaceuticals and other compounds and the problems associated with other well established borane adduct hydroboration agents, e.g., low concentration and stability, high volatility, flammability, unpleasant odor, as discussed above, create a need for easy to handle, stable and environmentally benign hydroborating agents as discussed specifically below.
Thus, the search continues for effective, versatile borane-sulfide derivatives which are as effective as the commercially available reagents but which overcome the disadvantages of noxious odor, expense, volatility, and lack of water solubility. The present invention fulfills this longstanding need.